What is asphalt milling?
Milling is the controlled removal of pavement to a set depth. Instead of breaking up the whole road and hauling it away, a milling machine takes off only the worn top layer, often just the 1.5 to 3 inches that will be replaced, and leaves the rest of the pavement in place.
It goes by several names. The process is called milling, cold milling, cold planing, grinding or profiling. The machine is a milling machine, cold planer, asphalt grinder or road planer. All of these mean the same thing. "Cold" separates it from hot in-place recycling, which heats the pavement first; a milling machine cuts it at air temperature.
The same machines also mill concrete. They remove a thin layer to restore texture, cut out damaged sections, or take an old road down to its base before it is rebuilt.
How asphalt is milled, step by step
A milling crew is usually an operator, one or two ground workers and a line of dump trucks. Here is what happens on a typical mill and overlay.
Mark the area and set the depth
The crew marks where milling starts and stops, then sets the cutting depth. The grade control is set to follow the old surface, a string line or a 3D model, and to hold the cross-slope the new pavement needs for drainage.
Lower the drum into the pavement
Hydraulic legs lower the machine until the drum cuts to the target depth. The drum turns up-cut: each tooth enters at the bottom of the cut and sweeps up and forward, breaking the asphalt into small pieces rather than lifting it in slabs.
Spray water on the teeth
A spray bar inside the drum housing wets the cutting teeth and the broken asphalt. The water keeps the carbide tips from overheating and holds down the dust.
Convey the millings into a truck
Paddles in the middle of the drum throw the millings onto a collecting conveyor, which hands them to the long loading conveyor. A dump truck drives ahead of the machine and is filled on the move. A large machine can fill a truck in a few minutes, so trucking often sets the pace.
Leave a clean, textured surface
The moldboard behind the drum scrapes up loose material, and the rear tracks follow in the fresh cut. A sweeper cleans up what is left. The grooves in the milled surface help the new asphalt grip.
Tack and pave
Before paving, a tack coat (a thin spray of asphalt emulsion) is applied so the new layer bonds to the milled surface. Then the paver lays the new asphalt and rollers compact it. Milled lanes should be paved soon, because the rough surface and the drop-off at its edge are hard on traffic.
Parts of a milling machine
Every cold planer, from a compact parking-lot machine to a full-lane highway mill, has the same basic parts. Click See it in 3D to jump to each one in the model.
- Cutting drum
- A steel cylinder as wide as the cut, studded with carbide-tipped teeth (also called picks or bits) in spiral rows. A 7-foot drum at standard spacing carries roughly 150 to 200 teeth. The spirals sweep the broken asphalt toward the middle of the drum.See it in 3D
- Teeth and holders
- Each tooth sits in a holder welded to the drum and spins in it as it cuts, so it wears evenly. Teeth wear quickly in hard, abrasive aggregate and are changed every day, often several times. Fine-milling and micro-milling drums space the teeth closer together for a smoother surface.See it in 3D
- Drum housing and moldboard
- The housing encloses the drum. Side plates ride on the old surface and keep the edge of the cut clean, and the moldboard behind the drum scrapes up loose millings.See it in 3D
- Water spray system
- A water tank, pump and spray bar cool the teeth and keep down the dust. Large machines carry several hundred to about 1,000 gallons and refill from a water truck.See it in 3D
- Collecting conveyor
- A short conveyor at the front of the housing catches the millings the drum throws forward and carries them under the machine.See it in 3D
- Loading conveyor
- A long conveyor boom that raises, lowers and swings to fill the truck ahead. On a few machines it loads from the back instead.See it in 3D
- Tracks and leveling legs
- Four crawler tracks (three wheels or tracks on many small machines) each sit on a hydraulic leg. The legs set the cutting depth and keep the machine level. The rear tracks run in the fresh cut.See it in 3D
- Grade and slope control
- Depth sensors on each side of the drum and a slope sensor hold the cut to the right depth and cross-slope, following the old surface, a string line, an averaging ski or a 3D system.See it in 3D
- Engine
- A diesel engine that drives the drum through a belt and gearbox and powers the hydraulics. Large half-lane machines run about 500 to 1,000 hp or more.See it in 3D
Why mill before repaving?
A plain overlay puts new asphalt on top of the old surface. Mill and overlay grinds some of it off first. Milling costs more, but on many jobs it is the right call:
- It keeps the finished height. Every overlay raises the surface. Where curbs, gutters, drains, door thresholds and driveway aprons fix the height, the old surface has to come off first, or water and the transitions end up in the wrong place.
- It removes the damaged layer. Cracked, raveled or oxidized asphalt is taken off instead of being buried, so its cracks are less likely to reflect up through the new layer.
- It fixes the shape. Milling can take out ruts, shoves and bumps, and restore cross-slope, so the new layer goes down at an even thickness on a true surface.
- It gives the new layer something to grip. The textured surface and a tack coat bond the overlay to the pavement below.
- It recycles the old pavement. The millings go back to an asphalt plant as reclaimed asphalt pavement (RAP), or are sold for driveways and rural roads.
Milling only fixes the surface. If the base under the asphalt is failing, with alligator cracking, deep ruts or soft spots, those areas need full-depth repair first, or the new surface will fail the same way. See asphalt paving vs. overlay for how to tell which one a lot needs.
Milling machine sizes
Milling machines are sized by drum width. Ranges below are typical across manufacturers, not the specification of any model.
| Machine | Cutting width | Typical depth | Used for |
|---|---|---|---|
| Skid-steer cold planer attachment | About 1 to 4 ft | Up to about 6 in | Patches, utility cuts, trip hazards, small repairs |
| Compact milling machine | About 1.5 to 4 ft | Up to about 8 to 12 in | Parking lots, edges, around manholes and curbs, patch prep |
| Half-lane machine | About 6.5 to 7.5 ft | Up to about 12 in | Most street, road and large parking lot work |
| Full-lane machine | About 12 to 14 ft | Up to about 12 in or more | Highways, interstates and airport runways |
The 3D model above is a half-lane, front-loading machine with four tracks, the most common setup on road jobs.
How much asphalt does milling remove?
In place, compacted asphalt weighs about 145.2 lb per cubic foot, so every square yard milled 1 inch deep removes about 109 lb of material. A 10,000 ft² parking lot milled 2 inches deep produces about 121 tons of millings, or about 7 loads at 20 tons per truck. The same 10,000 ft² milled 1.5 inches deep is about 91 tons.
Millings fluff up once they are broken, so a truckload fills more space than the same weight of pavement did. Truck counts are planned by weight. The asphalt calculator uses the same density to turn an area and depth into tons, and the trucking calculator works out how many trucks keep a machine busy.
Most millings go back to an asphalt plant, where they are crushed, screened and added to new mix as RAP. See where RAP enters the plant in how asphalt is made. Millings are also sold as a cheap surface for driveways and lots: recycled asphalt millings covers buying and laying them, and the gravel calculator has an asphalt millings setting for working out how many tons to order.
What does asphalt milling cost?
On a parking lot, milling typically adds about $1.00 to $2.50 per square foot on top of the overlay, and a complete mill and overlay runs about $4.00 to $9.00 per square foot as a 2026 national planning range. Depth, the size of the job, how far the millings are hauled, and whether the contractor credits their value all move the price. Small jobs usually carry a mobilization charge for bringing the machine in, which can set the price on its own.
For the full breakdown, with worked examples and sources, see asphalt overlay cost. To estimate the asphalt for the new layer, use the asphalt calculator.
Asphalt milling questions
What is an asphalt milling machine called?
It is called a milling machine, cold planer, cold milling machine, asphalt grinder, road planer or profiler. They all mean the same machine: a self-propelled machine with a rotating, toothed drum that grinds off a set depth of pavement and loads it into a truck.
How is asphalt milled?
The machine lowers a spinning drum covered in carbide teeth into the pavement to a set depth. The teeth break the asphalt into small pieces, water sprayed on the drum keeps the dust down, and conveyors carry the millings into a dump truck driving ahead. Sensors hold the depth and slope, and the machine leaves a level, grooved surface ready for a tack coat and new asphalt.
How deep can a milling machine cut?
Large milling machines can cut about 12 inches or more in one pass, and skid-steer attachments up to about 6 inches. Most mill-and-overlay jobs remove only about 1.5 to 3 inches, the depth of the layer being replaced.
Is milling the same as grinding asphalt?
Yes. Grinding, milling, cold milling, cold planing and profiling all describe removing pavement with a rotating toothed drum. "Grinding" is more common in conversation and "milling" or "cold planing" in specifications.
What is the difference between mill and overlay and an overlay?
An overlay places new asphalt on the existing surface and raises it. Mill and overlay grinds off part of the old surface first, so the new layer replaces it instead of sitting on top. Milling keeps curbs, drains and doorways at the right height, removes the damaged layer and costs more: roughly $4.00 to $9.00 per square foot for mill and overlay versus $2.00 to $5.00 for a parking lot overlay.
Can you drive on milled asphalt?
Yes, and milled roads are often open to traffic for a short time before paving. The surface is rough and noisy, loose millings can kick up, and the drop-off at the edge of the cut needs warning signs. It should be paved soon, because the thin remaining layer can be damaged by traffic and weather.
What is micro-milling?
Micro-milling uses a drum with teeth spaced much closer together than a standard drum, leaving a much smoother surface. It is used to remove a very thin layer, correct small surface defects or prepare a surface for a thin overlay or surface treatment.
How much does a milling machine cost?
Skid-steer cold planer attachments are the least expensive option. Compact and half-lane milling machines are major equipment purchases, and new large machines commonly run from several hundred thousand dollars to over $1 million. Most property owners never buy one. They hire a paving or milling contractor, who brings the machine for the job.
A typical machine, not every machine: The 3D model and figures describe a typical half-lane milling machine and common practice. Machines differ by manufacturer and model, and depths, speeds and prices on a real job depend on the pavement, the specification and the contractor.